1. Field of the Invention
The present invention relates to a laminated inductor array-having a plurality of inductors.
2. Description of the Related Art
A conventional laminated inductor array of the type shown in FIG. 9 is known. The laminated inductor array 1 includes magnetic sheets 2 on the surface of which coil conductors 3a-6e are provided. The coil conductors 3a-3e are electrically connected in series through via holes 12 provided in the magnetic sheets 12 to constitute a spiral inductor L1. Similarly, coil conductors 4a-4e, 5a-5e, and 6a-6e are electrically connected in series through via holes 12 provided in the magnetic sheets 12 to constitute spiral inductors L2, L3, and L4, respectively.
The magnetic sheets 2 are stacked on each other in order as shown in FIG. 9, and after magnetic cover sheets (not illustrated) having no conductor provided thereon, have been disposed on the top and bottom surfaces of the stacked magnetic sheets 2, they are integrally sintered to form a laminated body 15 as shown in FIG. 10. On the front and back surfaces of the laminated body 15, external electrodes 21a-24a and 21b-24b of the inductors L1-L4 are provided, respectively.
In the laminated inductor array 1 having the above-described construction, to provide a small-sized inductor array, when the inductors L1-L4 are disposed close to each other inside the laminated body 15, the magnetic path of each of the inductors L1-L4 interferes with one another, and the mutual magnetic coupling between the inductors L1-L4 becomes too large to disregard the coupling. As a result, the inductors L1-L4 inside the laminated body 15 often have different values of inductance.
Generally, the spiral inductors L1 and L4 located adjacent the left and right end surfaces of the laminated body 15 have less inductance, because the magnetic paths are narrowed at the end surfaces. In particular, as in the spiral inductor L4, when the number of the coil conductors 6b, 6c, and 6d on the left side in FIG. 11 is three and the number of the coil conductors 6a, 6b, 6d, and 6e on the right side in FIG. 11 is four, on the side of the end surface of the laminated body 15 where the number of the coil conductors is greater, the inductance is less than where the number of coil conductors is fewer, as explained in the following and the inductances become different between the inductors L1 and L4. That is, in each of the inductors L1-L4, the greater the number of the coil conductors, the larger the potential inductance is, and when the effective area of the magnetic path of coil conductors of a greater number as in the inductor L4 is reduced, the inductance is further decreased.
To overcome the above-described problems, preferred embodiments of the present invention provide a laminated inductor array including a plurality of inductors provided in a laminated body and which inductors have minimal variations in the inductance values thereof.
A laminated inductor array according to a preferred embodiment of the present invention includes a laminated body including a plurality of magnetic layers and a plurality of coil conductors provided thereon, a plurality of spiral inductors defined by the coil conductors which are electrically connected to one another and which are aligned in the laminated body, and external electrodes provided on the surfaces of the laminated body and connected to a lead-out end portion of each of the spiral inductors. In the laminated inductor array, in the direction of alignment of the spiral inductors, the number of the coil conductors on an end of the spiral inductor located at one end portion of the laminated body is equal to the number of coil conductors on an end of the spiral inductor located at the other end portion of the laminated body.
Further, a laminated inductor array according to another preferred embodiment of the present invention is constructed such that, in the direction of alignment of spiral inductors, at least a pattern of the coil conductor of the spiral inductor located at one end portion of the laminated body is symmetric about a central line with respect to a pattern of the coil conductor of the spiral inductor located at the other end portion of the laminated body.
Furthermore, a laminated inductor array according another preferred embodiment of the present invention is constructed such that, in the direction of alignment of spiral inductors, one lead-out portion of the respective spiral inductors located at one end portion and the other end portion of the laminated body respectively is led out from the middle of the respective spiral inductors.
Generally, the effective area of the magnetic path of two spiral inductors located at the end portions of a laminated body are reduced on the side of the end surfaces of the laminated body. However, because the number of the coil conductors on the end surface of a spiral conductor located at one end portion of a laminated body is equal to the number of the coil conductors on the end surface of a spiral conductor located at the other end portion of the laminated body, the decreased inductance value of the two spiral inductors located at the end portions of the laminated body is substantially equal and the inductance value of both inductors is therefore substantially equal.
Other features, elements, characteristics and advantages of preferred embodiments of the present invention will become apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.